The OptCom group has carried out a ground-breaking experiment of ultra-long haul transmission, proving the effectiveness of the so-called “symbol rate optimization” (SRO) strategy to improve system  performance. 19 PM-QPSK channels at 128 Gb/s were sent over a link with 110 km span length and EDFA-only amplification. The fiber was PSCF, provided by SEC (Sumitomo Electric Industries). A system reach of over 14,200 km was obtained, with a 12.5% reach gain obtained through SRO, vs. conventional single-carrier transmission. SRO was implemented by subdividing each channel into subcarriers.
Such distances have become important since the arctic route from Europe to Asia has been opened by the Arctic Fibre cable, which will connect London to Tokyo, spanning over 15,000 km.

The research has been presented at the European Conference on Optical Communications (ECOC). The presentation is available here for download.